1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for handling a barred cell in a wireless communication system.
2. Discussion of the Related Art
First, a network structure of a Universal Mobile Telecommunications System (UMTS) will be described with reference to FIG. 1.
FIG. 1 is a diagram showing a network structure of a UMTS. As shown in FIG. 1, the UMTS includes a user equipment (UE), a UMTS terrestrial radio access network (UTRAN) and a core network (CN). The UTRAN includes one or more radio network sub-systems (RNSs) and each RNS includes one radio network controller (RNC) and one or more base stations (Node Bs) managed by the RNC. One or more cells may exist per a single base station.
Next, the structure of a radio protocol used in the UMTS will be described with reference to FIG. 2. FIG. 2 is a diagram showing the structure of the radio protocol used in the UMTS. Pairs of radio protocol layers exist in the UE and the UTRAN, and perform data transfer over an air interface. In the radio protocol layers, a physical (PHY) layer, which is a first layer, is responsible for data transfer over an air interface using various radio transfer technologies. The PHY layer is connected to a medium access control (MAC) layer, which is a higher layer, through a transport channel, and the transport channel is divided into a dedicated transport channel and a common transport channel depending on whether or not the channel is shared.
A MAC layer, a radio link control (RLC) layer and a broadcast and multicast control (BMC) layer exist in a second layer. The MAC layer maps various logical channels to various transport channels and performs logical channel multiplexing to map a plurality of logical channels to one transport channel.
The MAC layer is connected to the RLC layer, which is a higher layer, through a logical channel. The logical channel is divided into a control channel for transmitting information on a control plane and a traffic channel for transmitting information on a user plane, according to the kind of transmitted information. Examples of the control channel include a Common Control Channel (CCCH) logical channel for transmitting common control information, a Dedicated Control Channel (DCCH) logical channel for transmitting control information to a specific UE, a Broadcast Control Channel (BCCH) logical channel for receiving system information commonly applied to a cell, a Paging Control Channel (PCCH) for receiving a paging message, etc. A Dedicated Traffic Channel (DTCH) for transferring data of the user plane to a specific UE exists in the traffic channel.
In addition, the MAC layer is divided into a MAC-b sublayer, a MAC-d sublayer, a MAC-c/sh sublayer, a MAC-hs/ehs sublayer, and a MAC-e/es or a MAC-i/is sublayer, according to the kind of the managed transport channel. The MAC-b sublayer is responsible for management of a Broadcast Channel (BCH) which is a transport channel for broadcasting system information, the MAC-c/sh sublayer is responsible for management of a Forward Access Channel (FACH) common transport channel shared with the other UEs, and the MAC-d sublayer is responsible for management of a Dedicated Channel which is a dedicated transport channel of a specific UE. In addition, the MAC-hs/ehs sublayer manages a High Speed Downlink Shared Channel (HS-DSCH) for high-speed downlink data transmission and the MAC-e/es or MAC-i/is sublayer manages an Enhanced Dedicated Channel (E-DCH) which is a transport channel for high-speed uplink data transmission.
The RLC layer guarantees Quality of Service (QoS) of a Radio Bearer (RBs) or data transmission. The RLC has one or two independent RLC entities for each RB in order to guarantee the QoS of the RB. In order to guarantee various QoSs, three operation modes, i.e., a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode (AM), are provided. In addition, the RLC is responsible for adjustment of a data size to suit data transmission over an air interface and is responsible for segmentation and concatenation of data received from a higher layer.
A Packet Data Convergence Protocol (PDCP) layer is located at a high level of the RLC layer and enables data transmitted as IP packets such as IPv4 or IPv6 packets to be efficiently transmitted over an air interface with a narrow bandwidth. The PDCP layer performs a header compression function to transmit only necessary information in a header part of data, thereby increasing transfer efficiency of the air interface. Since the PDCP layer has header compression as a basic function, the PDCP layer exists in a packet switched (PS) region and one PDCP entity exists per RB in order to provide an efficient header compression function to each PS service. However, if the PDCP layer exists in a circuit switched (CS) region, the header compression function is not provided.
In the second layer, a Broadcast/Multicast Control (BMC) layer is located at a level above the RLC layer so as to perform a function for scheduling a cell broadcast message and broadcasting the cell broadcast message to UEs located in a specific cell.
A Radio Resource Control (RRC) layer located at the lowermost level of the third layer is defined only in the control plane and is responsible for control of the parameters of the first layer and the second layer in association with configuration, re-configuration and release of Radio Bearers (RBs), and is responsible for control of the logical, transport and physical channels. The RB is a logical path that the first and second layers of the radio protocol provide for data communication between the UE and the UTRAN. Generally, Radio Bearer (RB) configuration means that a radio protocol layer necessary to provide a specific service and channel characteristics are defined and their detailed parameters and operation methods are configured.
A Non Access Stratum (NAS) layer located at a higher level of the third layer includes a Mobility Management (MM) entity and a Connection Management (CM) entity. The MM entity performs a Temporary Mobile Subscriber Identity (TMSI) reassignment process, an authentication process, a UE identification process, an International Mobile Subscriber Identity (IMSI) appending process, etc., identifies each UE, and manages several UEs. In addition, the MM entity manages current location information of a UE through a location information updating process. The CM entity provides and controls a service provided by a network. Accordingly, the CM entity performs connection establishment, management and termination of a voice call, connection establishment, management and termination of session corresponding to data communication and provision and control of a Short Message Service (SMS), or connection establishment, management and termination of a supplementary service.
Next, a dual cell High Speed Packet Access (HSPA) will be described. The dual cell HSPA indicates technology of transmitting data, which was transmitted performed by a UE through an E-DCH only using one frequency in the past, using two frequencies so as to increase data transmission rate to twice that of the related art. An operation for transmitting data using two frequencies by the UE is referred to as a dual cell E-DCH operation. In addition, in a downlink, in the related art, the UE received a High Speed Downlink Shared Channel (HS-DSCH) using one frequency. An operation for simultaneously receiving data using two frequencies so as to double the data reception rate is referred to as a High Speed Downlink Packet Access (HSDPA) operation.
In the related art, an active set is defined as a set of cells having both an uplink radio link and a downlink radio link in one cell. Accordingly, in a UE which performs a dual cell HSDPA operation, a first cell having both one uplink radio link and one downlink radio link belongs to the active set and a second cell having only a downlink radio link does not belong to the active set.
If the UE which performs the dual cell HSDPA operation receives an RRC connection release message from a higher layer due to authentication failure, the UE releases all connected radio resources and regards the first cell belonging to the active set as a barred cell before going to an idle mode. The second cell does not belong to the active set and thus is not regarded as the barred cell.
Accordingly, when the UE selects a new cell after going to the idle mode, the UE may reselect the second cell if the radio environment of the second cell is good. However, since the authentication process failed in the second cell, the authentication process may fail even when connection establishment with the second cell is performed. Thereafter, a higher layer of the UE transmits an RRC connection release message to an RRC layer and the UE regards the second cell as the barred cell and does not reselect the second when selecting a new cell. That is, an additional unnecessary cell selection process may be performed during the dual cell HSDPA operation.
As described above, in the related art, an unnecessary cell selection process may be performed.